Near-inertial waves in the wake of 2011 Typhoon Nesat in the northern South China Sea
-
摘要: 2011年9月台风“纳沙”经过南中国海北部的锚定潜标, 该潜标观测到上层海洋的流速和温度响应。上层海洋的响应主要为台风尾迹处的斜压近惯性内波。近惯性流速呈现表层强化和顺时针极化的特征, 但是水深300m处近惯性流速依然达5cm/s。近惯性内波的频率为0.7099周每天, 比局地惯性频率高0.025f, 其中f为局地惯性频率。根据近惯性水平动能演化得到的近惯性内波e折时间为10天。近惯性流速的垂向分布呈现明显的位相上传, 表明下传的群速度和能量, 垂向相速度和群速度分别为0.27和0.08cm/s, 对应的垂向波长为329m。谱分析的结果表明在台风输入上混合层能量的再分配过程中近惯性内波起主要作用。垂向模态方程数值解和经验正交函数分解的结果表明近惯性内波以第二斜压模态为主(方差贡献81%), 其水平相速度和波长分别为3.50m/s和420km。由于地转的作用近惯性内波的水平相速度显著大于内重力波, 定量分析表明“蓝移”为0.025f的近惯性内波的相速度为相同层结下内重力波的4.6倍。Abstract: In September 2011, Typhoon Nesat passed over a moored array of instruments recording current and temperature in the northern South China Sea (SCS). A wake of baroclinic near-inertial waves (NIWs) commenced after Nesat passed the array. The associated near-inertial currents are surface-intensified and clockwise-polarized. The vertical range of NIWs reached 300 m, where the vertical range is defined as the maximum depth of the horizontal near-inertial velocity 5 cm/s. The current oscillations have a frequency of 0.709 9 cycles per day (cpd), which is 0.025f higher than the local inertial frequency. The NIWs have an e-folding time-scale of 10 d based on the evolution of the near-inertial kinetic energy. The depth-leading phase of near-inertial currents indicates downward group velocity and energy flux. The estimated vertical phase velocity and group velocity are 0.27 and 0.08 cm/s respectively, corresponding to a vertical wavelength of 329 m. A spectral analysis reveals that NIWs act as a crucial process to redistribute the energy injected by Typhoon Nesat. A normal mode and an empirical orthogonal function analysis indicate that the second mode has a dominant variance contribution of 81%, and the corresponding horizontal phase velocity and wavelength are 3.50 m/s and 420 km respectively. The remarkable large horizontal phase velocity is relevant to the rotation of the earth, and a quantitative analysis suggests that the phase velocity of the NIWs with a blue-shift of 0.025f overwhelms that of internal gravity waves by a factor of 4.6.
-
Key words:
- near-inertial waves /
- South China Sea /
- Typhoon Nesat
-
Amante C, Eakins B W. 2009. ETOPO1 1 arc-minute global relief model: procedures, data sources and analysis. Boulder Colorado: National Geophysical Data Center, NOAA, doi: 10.7289/V5C8276M Brink K H. 1989. Observations of the response of thermocline current to a hurricane. Journal of Physical Oceanography, 19(7): 1017-1022 Brooks D A. 1983. The wake of Hurricane Allen in the western Gulf of Mexico. Journal of Physical Oceanography, 13(1): 117-129 Chang S W. 1985. Deep ocean response to hurricanes as revealed by an ocean model with free surface: Part I. Axisymmetric case. Journal of Physical Oceanography, 15(12): 1847-1858 Chu Peter C, Veneziano J M, Fan Chenwu, et al. 2000. Response of the South China Sea to tropical cyclone Ernie. Journal of Geophysical Research, 105: 13991-14009 Cuypers Y, Vaillant X L, Bouruet-Aubertot P, et al. 2013. Tropical storm induced near-inertial internal waves during the Cirene experiment: energy fluxes and impact on vertical mixing. Journal of Geophysical Research: Oceans, 118: 358-380 Fofonoff P, Millard R C Jr. 1983. Algorithms for computation of fundamental properties of seawater. Unesco Technical Papers in Marine Science, 44: 53 Fu Lee-Lueng. 1981. Observations and models of inertial oscillations in the deep ocean. Reviews of Geophysics, 19(1): 141-170 Garrett C. 2001. What is the “near-inertial” band and why is it different from the rest of the internal wave spectrum? Journal of Physical Oceanography, 31(4): 962-971 Gill A E. 1982. Atmosphere-Ocean Dynamics. New York: Academic Press Gill A E. 1984. On the behavior of internal waves in the wakes of storms. Journal of Physical Oceanography, 14: 1129-1151 Keisuke T, Shojik K, Hirotaka O, et al. 1993. Observation of temperature and velocity from a surface buoy moored in the Shikoku Basin (OMLET-88)-An oceanic response to a typhoon. Journal of Oceanography, 49: 397-406 Leaman K D, Sanford T B. 1975. Vertical energy propagation of inertial waves: a vector spectral analysis of velocity profile. Journal of Geophysical Research, 80(15): 1975-1978. Liu Junliang, Cai Shuqun, Wang Sheng'an. 2010. Currents and mixing in the northern South China Sea. Chinese Journal of Oceanology and Limnology, 28(5): 974-980 Liu Junliang, Cai Shuqun, Wang Sheng'an. 2011. Observations of strong near-bottom current after the passage of Typhoon Pabuk in the South China Sea. Journal of Marine Systems, 87(1): 102-108 Pollard R T. 1980. Properties of near-surface inertial oscillations. Journal of Physical Oceanography, 10: 385-398 Price J F. 1981. Upper ocean response to a hurricane. Journal of Physical Oceanography, 11(2): 153-175 Price J F. 1983. Internal wave wake of a moving storm: Part I. Scales, energy budget and observations. Journal of Physical Oceanography, 13(6): 949-965 Price J F, Sanford T B, Forristall G Z. 1994. Forced stage response to a moving hurricane. Journal of Physical Oceanography, 24: 233-260 Rossby C G. 1938. On the mutual adjustment of pressure and velocity distributions in certain simple current systems: Ⅱ. Journal of Marine Research, 1: 239-263 Shay L K, Chang S W, Elsberry R L. 1990. Free surface effects on the near-inertial ocean current response to a hurricane. Journal of Physical Oceanography, 20: 1405-1424 Shay L K, Elsberry R L. 1987. Near-inertial ocean current response to Hurricane Frederic. Journal of Physical Oceanography, 17(8): 1249-1269 Sun Lu, Zheng Quan'an, Tang Tswen-Yung, et al. 2012. Upper ocean near-inertial response to 1998 Typhoon Faith in the South China Sea. Acta Oceanologica Sinica, 31(2): 25-32 Wang Gang, Qiao Fangli, Hou Yijun, et al. 2008. Response of internal waves to 2005 Typhoon Damrey over the northwestern shelf of South China Sea. Journal of Ocean University of China, 7(3): 251-257 Welch P. 1967. The use of fast Fourier transform for the estimation of power spectra: a method based on time averaging over short, modified periodograms. Audio and Electroacoustics, IEEE Transactions, 15(2): 70-73 Zheng Quan'an, Lai R J, Huang N E, et al. 2006. Observation of ocean current response to 1998 Hurricane Georges in the Gulf of Mexico. Acta Oceanologica Sinica, 25(1): 1-14
点击查看大图
计量
- 文章访问数: 1419
- HTML全文浏览量: 40
- PDF下载量: 1333
- 被引次数: 0